Field
Embodiments described herein generally relate to apparatus and methods for substrate processing using microwave radiation.
Description of the Related Art
Thin films are the major components of semiconductor devices. Typical thin films used in the semiconductor industry can be in the form of porous dielectrics, low resistance metals, polymeric materials and high-k dielectrics. During flip chip and wafer level packaging, large quantities of polymers are patterned and used as repassivation layers prior to the Under-Bump Metallization (UBM) or redistribution layer (RDL) metallization element. Another example are the highly porous low-k dielectrics, widely used as inter-metal dielectric films in high performance semiconductor devices.
A typical process flow after the developing of a patterned polymer films includes curing of the film and subsequent PVD deposition of the UBM/RDL. In typical processing, polymeric film curing and PVD barrier seed deposition are carried out on separate equipment. The curing process is typically done thermally in conventional oven. This introduces a vacuum break between the processes, resulting in moisture adsorption in the polymeric film.
If the absorbed gaseous impurities in the dielectric films (e.g. H2O) are not removed prior to the metal deposition, they will outgas during the PVD process as a result of the higher temperatures achieved during plasma processes. Consequently, the substrate should be degassed to prevent outgassed impurities from affecting the quality of the PVD metal layer. Tantalum, for example, may form Tantalum oxide in the presence of certain impurities which is not an optimal barrier material to prevent Copper diffusion. In another example, such as for packaging metallization (e.g. UBM applications), if H2O is not removed prior to a pre clean element (by sputter etch), outgassing of the H2O will occur leading to the formation of other unwanted oxides, such as Aluminum oxide. Aluminum oxide can form on the aluminum bondpad, giving rise to undesirable high contact resistance.
Thus, there is a continuing need in the art for methods and apparatus which allow for efficient curing of the film while minimizing gas and moisture absorption.
Further, due to the nature of CVD process, the incorporation of impurities, such as from the by-products of chemical reactions or residual gases, will significantly affect the resulting film properties. For example, impurities such as moisture (H2O) and CO can be misincorporated into porous low-k dielectric, which will increase the k value. In a typical semiconductor process flow, PVD metal films are usually deposited on a dielectric layers or a polymetric buffer layer.
If the absorbed gaseous impurities in the dielectric films (e.g. H2O) are not removed prior to the metal deposition, they will outgas during the PVD process as a result of the higher temperatures achieved during plasma processes. Consequently, outgassed impurities can affect the quality of the PVD metal layer. Tantalum, for example, may form Tantalum oxide in the presence of certain impurities which is not an optimal barrier material to prevent Copper diffusion. In another example, such as for packaging metallization (e.g. UBM applications), if H2O is not removed prior to a pre clean element (by sputter etch), outgassing of the H2O will occur leading to the formation of other unwanted oxides, such as Aluminum oxide. Aluminum oxide can form on the Aluminum bondpad, giving rise to undesirable high contact resistance.
To avoid outgassing during PVD processing, a degas element (by convection heating) is used prior to preclean and metallization to remove any moisture from the underlying substrate. Standard degas procedures generally include heating of the substrate with the affected layer for a period of time, such that the absorbed gases and impurities can escape without affecting deposition in later elements. The heat is usually generated by resistive heating element or lamp, and then transferred to the substrate and thin films by convection. However, due to the ever increasing porosity of dielectric films, as well as highly moisture adsorbent polymers used in packaging applications, long degas times are generally required to completely remove the moisture from the films. Long degas times limit the productivity of a PVD process. Further, standard thermal processing can easily bring modern films to a temperature which produces oxygen-containing secondary gases or leads to glass transition of the layer.
Thus, there is a need in the art for methods and apparatus which allow for efficient degassing of the film while maintaining heat with the thermal processing ranges of the deposited film.